SC STANDARD B-6. 2: Students will demonstrate an understanding of the way populations are affected by density-dependent factors & density-independent factors.

 CN page  Topic: Populations  EQ: What factors affect population size?

How do Populations Grow?  3 important characteristics of a population are its :  geographic distribution  density  growth rate

Geographic Distribution  is the range or area where the organism is found

Hooker’s Manzanita  found in maritime chaparrel (threatened habitat due to development)  Central California (Monterrey County)

Franklin’s Bumble Bee  Most restricted geographic distribution of any known bee  Between Pacific coast & Sierra Nevada in Oregon & northern California

Density  population density: the # of individuals per unit area  Density is one of the main characteristics that describes a natural population.

Growth Rate  3 factors affect population growth:  1. # of births  2. # of deaths  3. # of individuals that immigrate or emmigrate  Immigration: movement of individuals into an area  Emmigration: movement of individuals out of an area

EXPONENTIAL GROWTH  growth pattern in which the individuals in a population reproduce at a constant rate  Under ideal conditions with unlimited resources, a population will grow exponentially

LOGISITIC GROWTH  growth pattern in which a population’s growth rate slows or stops following a period of exponential growth  carrying capacity: largest # of individuals of a population that a given environment can support

Carrying Capacity Graph

Limiting Factors to Growth  In respect to populations a limiting factor is anything that causes population growth to decrease.  Limiting factors are either:  Density-Dependent  Density-Independent

Density-Dependent Limiting Factors  limiting factor that depends on population size  become limiting only when population density reaches a certain level  Include:  1. competition  2. predation  3. parasitism & disease

1. Competition When populations become crowded members of same or different species compete for food, shelter, mates, space, sunlight

2. Predation  Predator-Prey relationships mechanism of population control

3. Parasitism & Disease  Parasites take nourishment from their host  host weakens  does not usually die

Density-Independent Factors  affect all the populations in similar ways, regardless of #’s  Forest fires  Floods  Seasonal cycles  Human interference (clear-cutting, damming river)

Human Population Growth  Population of humans on Earth increases with time

Patterns of Population Growth  Birth rates, death rates, & the age structure of a population help predict why some countries have high growth rates while other countries grow slowly.

The Demographic Transition  the change in a population from high birth & death rates to low birth & death rates

 Complete concept map from page 134 of book on page of notebook (landscape)